1. Field of the Invention
The present invention relates to a support for a gas-phase oxidation catalyst and a process for its production, a gas-phase oxidation catalyst, and a process for producing acrylic acid.
2. Description of the Prior Art
Gas-phase catalytic oxidation is suitable for large-scale production at a lower cost. Therefore, gas-phase catalytic oxidation is now widely used for the production of variable basic chemicals from petrochemical feedstocks on an industrial scale. For example, ethylene oxide is produced by the gas-phase catalytic oxidation of ethylene, and maleic anhydride is produced by the gas-phase catalytic oxidation of benzene or n-butane. In addition, (meth)acrylic acid is produced by gas-phase catalytic oxidation starting from propane or propylene, or at least one kind of compound selected from isobutylene, tert-butanol, and methyl tert-butyl ether, and providing (meth)acrylic acid through (meth)acrolein.
For these processes of gas-phase catalytic oxidation, there is usually used a catalyst comprising an active catalytic component such as a complex oxide or heteropoly acid, which is supported on an inert support such as alumina or silica.
However, when conventional gas-phase oxidation catalysts using inactive supports are used for production on an industrial scale, the yield of a final product is insufficient, and a decrease in catalytic activity is quick, thereby making catalyst life short. Therefore, the conventional gas-phase oxidation catalysts using inactive supports do not have necessarily have sufficient satisfactory catalytic performance.
Accordingly, for example, Japanese Patent Laid-open Publication No. 8-47641 discloses a method of improving the activity and stability of a catalyst by including a solid superacid, of which acid strength (H0) meets an inequality: H0≦−11.93, in a complex oxide catalyst containing molybdenum and vanadium as essential components when acrylic acid is produced by the gas-phase catalytic oxidation of acrolein. Further, Japanese Laid-open Patent Publication No. 8-47643 discloses a method of improving the activity and stability of a catalyst by including a solid superacid, of which acid strength (H0) of H0≦−11.93 in a complex oxide catalyst containing molybdenum and phosphorus as essential components when methacrylic acid is produced by the gas-phase catalytic oxidation or gas-phase catalytic oxidative dehydrogenation of at least one compound selected from methacrolein, isobutyraldehyde, and isobutyric acid.
However, in such methods using a solid superacid, a process for preparing the solid superacid is complicated, and the solid superacid is prepared separately. Therefore, these methods become expensive, and the production cost of catalyst is inevitably increased.